This invention relates to human follicle stimulating hormone receptor and its synthesis by recombinant DNA techniques.
Follicle stimulating hormone (FSH) is a pituitary-derived heterodimeric glycoprotein hormone which shares structural similarities with luteinizing hormone (LH) and thyroid stimulating hormone (TSH), both of which are also produced in the pituitary gland, and chorionic gonadotropin (CG), which is produced in the placenta. The hormones are relatively large (28-38 kilodaltons) and are composed of a common .alpha. subunit non-covalently bound to a distinct .beta. subunit that confers receptor binding specificity.
The cellular receptors for these hormones are known to be members of the G protein-coupled class of membrane-bound receptors which when activated stimulate an increase in the activity of adenylyl cyclase. This results in an increase in the level of the intracellular second messenger adenosine 3',5'-monophosphate (cAMP), which in turn causes increased steroid synthesis and secretion. Hydropathicity plots of the amino acid sequences of these receptors reveal three general domains: (1) a hydrophilic amino-terminal region, considered to be the amino-terminal extracellular domain, (2) seven hydrophobic segments of membrane-spanning length, considered to be the transmembrane domain, and (3) a carboxy-terminal region which contains potential phosphorylation sites (serine, threonine, and tyrosine residues), considered to be the carboxy-terminal intracellular or cytoplasmic domain. The glycoprotein hormone receptor family is distinguished from other G protein-coupled receptors, such as the .beta.2-adrenergic, rhodopsin, and substance K receptors, by the large size of the hydrophilic amino-terminal domain, which is involved in hormone binding.
The FSH receptor is expressed on testicular Sertoli cells and ovarian granulosa cells. While there has been a recognized need for providing essentially pure human FSH receptor, purification of naturally derived preparations is not practical and would not likely be sufficient to permit determination of the amino acid sequence. Recently, one group has cloned the cDNA encoding the rat FSH receptor, deduced the amino acid sequence, and expressed it in mammalian cells (Sprengel, Mol. Endocrinol. 4:525, 1990). Another group, attempting to clone the TSH receptor, apparently also cloned and identified a portion of the transmembrane region of the human FSH receptor (Parmentier, Science 246:1620, 1989).